Relay apparatus, communication system and communication method

ABSTRACT

Relay apparatuses read the attribute values of data, i.e., numerical information representing measurement values, calculation values, control values, etc., from receive buffers in which data received from ECUs connected thereto is stored, and create trunk frames containing the numerical information and transmit and receive trunk frames via trunk lines. The relay apparatuses derive numerical information from trunk frames received from the other relay apparatuses and renew the numerical information on the data stored in their respective databases using the derived numerical information.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP2009/003249 which has anInternational filing date of Jul. 10, 2009 and designated the UnitedStates of America.

BACKGROUND

1. Technical Field

The present invention relates to a communication system in which data istransmitted and received among a plurality of communication apparatuses.More particularly, the present invention relates to relay apparatuses, acommunication system including the relay apparatuses and a communicationmethod, capable of shortening the time required for data exchange byreducing the amount of communication so as to reduce communication loadin the case that data is exchanged among the relay apparatuses in acommunication system provided with the plurality of relay apparatusesfor relaying the transmission and reception of data.

2. Description of Related Art

In recent years, there has been used, in various fields, a system inwhich a plurality of communication apparatuses are connected, functionsare assigned to the respective communication apparatuses so that data isexchanged mutually among the communication apparatuses and variousprocesses are carried out in cooperation. For example, in the field ofvehicle-mounted LAN (local area network) on vehicles, ECUs (ElectronicControl Units) are used as communication apparatuses to carry outprocesses specific to the respective ECUs and to exchange data amongthem, whereby various functions are achieved in the system.

As the functions of the respective communication apparatuses arespecialized and the functions that can be carried out by the respectivecommunication apparatuses increase in number, the communicationapparatuses to be connected to communication media also increase innumber and type. Furthermore, since various functions are expected to becarried out in the system, it becomes necessary for the respectivecommunication apparatuses to share data and operate in cooperation,whereby the amount of data to be transmitted increases.

The increase in the amount of data to be transmitted and received via acommunication line may cause data delay or dropout due to collision.Significant data delay or dropout may be sometimes fatal to the drivingassistance functions of a vehicle, such as brake control using an ECU.

Accordingly, there has been generally used a configuration whichincludes a plurality of communication lines and in which ECUs areconnected to the respective communication lines. This configuration isadopted because wasteful use of communication lines can be suppressed bygrouping ECUs in which data is shared. Furthermore, anotherconfiguration has also been used in which, for the purpose of usingcommunication lines efficiently to cope with the increase in the type ofECUs, the ECUs are classified depending on the type of data to betransmitted and received and connected to communication lines,communication speeds of which are different. With these configurations,relay apparatuses for controlling data transmission and reception areconnected among different communication lines.

Even in the case that the communication apparatuses are divided into aplurality of groups, the amount of data to be transmitted to thecommunication lines is not reduced in a configuration in which the relayapparatuses transfer all the data required for the control of therespective communication apparatuses. Hence, Japanese Patent ApplicationLaid-Open No. 2007-300331 discloses a technology in which data receivedfrom each communication apparatus is stored once in a database, datarequired for each communication apparatus is read from the database andtransmitted as necessary, and data recorded in the databases istransmitted and received among the apparatuses having databases, wherebythe databases are shared.

SUMMARY

With the technology disclosed in Japanese Patent Application Laid-OpenNo. 2007-300331, a configuration is obtained in which the communicationapparatuses are divided into a plurality of groups, apparatuses havingdatabases are used to relay the transmission and reception of data amongdifferent groups, and the databases are shared, whereby data delay canbe reduced. In the case of this configuration in which the apparatuseshaving the databases are used to relay the transmission and reception ofdata among the different groups of the communication apparatuses, whenthe relay processing is required to be carried out at higher speed, theamount of communication among the relay apparatuses having the databasesis desired to be reduced.

In view of the circumstances described above, the present invention isintended to provide relay apparatuses, a communication system includingthe relay apparatuses and a communication method, capable of reducingthe amount of communication by virtue of a configuration in which, amongdata, each piece being formed of a pair of identification informationand numerical information corresponding to the identificationinformation, only the numerical information is combined appropriatelyand transmitted and received in the case of exchanging data among therelay apparatus having databases, whereby the amount of communicationcan be reduced.

A relay apparatus according to a first aspect of the present inventionis a relay apparatus connected to external apparatuses for transmittingand receiving data containing numerical information and identificationinformation of the numerical information, and equipped with means forreceiving data from at least one of the external apparatuses, means forstoring data in a database and means for transmitting data read from thedatabase to at least one of the external apparatuses, thereby relayingtransmission and reception of data among external apparatuses, the relayapparatus comprising means for creating a data frame containingnumerical information on one or a plurality of pieces of data receivedfrom at least one of the external apparatuses; means for transmittingthe created data frame to another relay apparatus; means for receiving adata frame from another relay apparatus; means for reading, in the casethat a data frame is received, numerical information contained in thereceived data frame; and means for renewing numerical information ondata in the database according to the read numerical information.

A relay apparatus according to a second aspect of the present inventionis a relay apparatus equipped with means for storing positions andinformation lengths of the numerical information contained in a dataframe for each number of pieces of numerical information contained inthe data frame and each data type specified depending on identificationinformation corresponding to the numerical information, andidentification information corresponding to the respective pieces of thenumerical information; means for transmitting information on the type ofdata frame when the data frame is transmitted to another relayapparatus; and means for specifying the type of a data frame when thedata frame is received from another relay apparatus, wherein, when adata frame is received from said another relay apparatus, numericalinformation is derived from the data frame on the basis of the specifiedtype.

A communication system according to a third aspect of the presentinvention is a communication system equipped with a plurality ofcommunication apparatus groups, each group being formed of a pluralityof communication apparatuses for transmitting and receiving datacontaining numerical information and identification information of thenumerical information; and a plurality of relay apparatuses to which oneor a plurality of communication apparatuses are connected in each of theplurality of communication apparatus groups and each of which isequipped with means for receiving data from at least one of thecommunication apparatuses, means for storing data in a database andmeans for transmitting data read from the database to at least one ofthe communication apparatuses, the plurality of relay apparatuses beingconnected mutually to relay transmission and reception of data among thecommunication apparatuses, wherein each of the relay apparatuses isequipped with means for creating a data frame containing numericalinformation on one or a plurality of pieces of data received from atleast one of the communication apparatuses; means for transmitting thecreated data frame to another relay apparatus; means for receiving adata frame from another relay apparatus; means for reading, in the casethat a data frame is received, numerical information contained in thereceived data frame, and means for renewing numerical information ondata in the own database of each relay apparatus using the readnumerical information.

A communication method according to a fourth aspect of the presentinvention is a communication method using a plurality of relayapparatuses to which one or a plurality of communication apparatuses areconnected in each of a plurality of communication apparatus groups, eachgroup being formed of the plurality of communication apparatuses fortransmitting and receiving data containing numerical information andidentification information of the numerical information, and which aremutually connected to relay transmission and reception of data amongcommunication apparatuses and each of which receives data from at leastone of the communication apparatuses of the group to which the relayapparatus is connected, stores data in a database, transmits data readfrom the database to at least one of the communication apparatuses,wherein each of the relay apparatuses creates a data frame containingnumerical information on one or a plurality of pieces of data receivedfrom at least one of the communication apparatuses, transmits thecreated data frame to another relay apparatus, reads, in the case that adata frame is received from another relay apparatus, numericalinformation contained in the received data frame, renews numericalinformation on data in the own database of each relay apparatus usingthe read numerical information, and reads data from the renewed databaseand transmits the read data to at least one of the communicationapparatuses of the group to which the relay apparatus is connected.

In the first, third and fourth aspects of the present invention, theexternal apparatuses (communication apparatuses) carry out transmissionand reception, and in the case that data stored in the databases of therelay apparatuses is formed of a pair of information, i.e., numericalinformation and identification information of the numerical information,and when the data in the databases is exchanged among the relayapparatuses, the data exchange is carried out by transmitting andreceiving data frames containing the numerical information. The largerthe number of data types is, the longer the information lengthrepresenting the identification information becomes, and the totalinformation length of the identification information becomes longerdepending on the number of pieces of data to be exchanged among therelay apparatuses. However, since the transmission and reception of theidentification information of each piece of data are omitted in thetransmission and reception among the relay apparatuses, the amount ofcommunication is reduced.

In the second aspect of the present invention, the relay apparatusstores the position of the numerical information contained in the dataframe and the identification information corresponding to the numericalinformation for each data type specified depending on the identificationinformation corresponding to the numerical information in the data frameand the number of pieces of numerical information. Hence, when a dataframe is transmitted among the relay apparatuses, the information on thetype of the data frame is transmitted, whereby the relay apparatushaving received the data frame can read the respective pieces ofnumerical information contained in the data frame.

In the case of the present invention, when the data in the own databaseof a relay apparatus is exchanged with that of another relay apparatusso that the data is relayed among different groups of externalapparatuses (communication apparatuses), the transmission ofidentification information corresponding to the numerical information onthe data contained in the database is omitted, whereby the amount ofcommunication among the relay apparatuses can be reduced. Since theamount of communication among the relay apparatuses is reduced, the timerequired for the exchange of the data in the databases of the relayapparatuses can be shorted, and the data exchange can be completed athigh speed. As a result, it is possible to ensure the uniformity of dataand the immediacy of the relay among the different groups of externalapparatuses.

The above and further objects and features will move fully be apparentfrom the following detailed description with accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a vehicle-mountedcommunication system according to the present embodiment;

FIG. 2 is a block diagram showing internal configurations of an ECU anda relay apparatus constituting the vehicle-mounted communication systemaccording to the present embodiment;

FIG. 3 is a flowchart showing an example of a procedure to be done inthe case that a control section of the relay apparatus constituting thevehicle-mounted communication system according to the present embodimentreceives a message;

FIGS. 4A and 4B are explanatory views showing format examples of a trunkframe transmitted by the control sections of the relay apparatusesconstituting the vehicle-mounted communication system according to thepresent embodiment;

FIG. 5 is an explanatory view showing examples of contents of acorrespondence table stored in a storage section of the relay apparatusconstituting the vehicle-mounted communication system according to thepresent embodiment;

FIG. 6 is a flowchart showing an example of a procedure in which trunkframes are transmitted and received among the relay apparatusesconstituting the vehicle-mounted communication system according to thepresent embodiment;

FIG. 7 is a flowchart showing an example of a procedure in which trunkframes are transmitted and received among the relay apparatusesconstituting the vehicle-mounted communication system according to thepresent embodiment;

FIG. 8 is an explanatory view schematically showing a process in whichdatabases of the relay apparatuses according to the present embodimentare renewed by the transmission and reception of trunk frames;

FIG. 9 is a flowchart showing another example of the procedure in whichtrunk frames are transmitted and received among the relay apparatusesconstituting the vehicle-mounted communication system according to thepresent embodiment; and

FIG. 10 is an explanatory view schematically showing another example ofthe process in which the databases of the relay apparatuses according tothe present embodiment are renewed by the transmission and reception oftrunk frames.

DETAILED DESCRIPTION

The present invention will be described below specifically on the basisof the drawings showing an embodiment thereof. In the embodimentdescribed below, a case will be described as an example in which acommunication system according to the present invention is applied to avehicle-mounted communication system in which a plurality of ECUs forcarrying out data transmission and reception are connected.

FIG. 1 is a view showing a configuration of the vehicle-mountedcommunication system according to the present embodiment. Thevehicle-mounted communication system includes ECUs (Electronic ControlUnits) 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1 d, 1 d, .. . , 1 e, 1 e, . . . , 1 f, 1 f, . . . which are communicationapparatuses for transmitting and receiving data and forms groups;communication lines 2 a, 2 b, 2 c, 2 d, 2 e and 2 f connected to thegroups of ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . , respectively, groupby group; relay apparatuses 3 a, 3 b and 3 c, respectively connected tocommunication lines 2 a, 2 b, 2 c, 2 d, 2 e and 2 f, for relaying datatransmission and reception among the ECUs 1 a, 1 a, . . . , 1 b, 1 b, .. . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, .. . ; and communication lines 4 for connecting the relay apparatuses 3a, 3 b and 3 c. The vehicle-mounted communication system according tothe present embodiment constitutes a trunk-type vehicle-mounted networkin which the plurality of groups of the ECUs 1 a, 1 a, . . . , 1 b, 1 b,. . . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f,. . . are connected with one another via the relay apparatuses 3 a, 3 band 3 c connected to the communication lines 4 serving as trunk lines.For clarity of description, the communication lines 2 a, 2 b, 2 c, 2 d,2 e and 2 f are hereafter referred to as branch lines 2 a, 2 b, 2 c, 2d, 2 e and 2 f, and the communication lines 4 are hereafter referred toas trunk lines 4.

The ECUs 1 a, 1 a, . . . are connected to the branch line 2 a, the ECUs1 b, 1 b, . . . are connected to the branch line 2 b, the ECUs 1 c, 1 c,. . . are connected to the branch line 2 c, the ECUs 1 d, 1 d, . . . areconnected to the branch line 2 d, the ECUs 1 e, 1 e, . . . are connectedto the branch line 2 e, and the ECUs 1 f, 1 f, . . . are connected tothe branch line 2 f. A bus type is used as a connection topology amongthe ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1 d, 1 d,. . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . via the branch lines 2 a, 2 b,2 c, 2 d, 2 e and 2 f. This is because the ECUs 1 a, 1 a, . . . , 1 b, 1b, . . . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1f, . . . transmit and receive data according to the CAN (controller areanetwork) protocol as described later. However, any connection topology,such as star topology or daisy-chain topology, may be used.

The daisy-chain topology is used for the connection topology among therelay apparatuses 3 a, 3 b and 3 c via the trunk lines 4. The relayapparatuses 3 a, 3 b and 3 c are equipped with storage areas serving asdatabases 31 a, 31 b and 31 c, respectively.

The relay apparatus 3 a, basically, stores data transmitted from theECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . connected thereto via the branchlines 2 a and 2 b in the database 31 a and transmits data read from thedatabase 31 a to the ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . .Furthermore, the relay apparatus 3 a transmits data received from theECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . to the other relay apparatuses 3b and 3 c and stores data received from the other relay apparatuses 3 band 3 c in the database 31 a. Similarly, the other relay apparatuses 3 band 3 c store data received from the other relay apparatuses 3 a, 3 band 3 c in the databases 31 b and 31 c. As a result, the databases 31 a,31 b and 31 c are synchronized so as to have the same contents, and therespective ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . connected to thedifferent branch lines 2 a, 2 b, 2 c, 2 d, 2 e and 2 f can use the samedata.

FIG. 2 is a block diagram showing internal configurations of the ECU 1 cand the relay apparatus 3 b constituting the vehicle-mountedcommunication system according to the present embodiment.

The ECU 1 c is equipped with a control section 10 for controlling theoperations of various components, a storage section 11 for storing datanecessary for control, and a communication control section 12 forcontrolling communication with the branch line 2 c. Since the internalconfigurations of the other ECUs 1 a, 1 b, 1 d, 1 e and 1 f are similarto that of the ECU 1 c, the detailed descriptions thereof are omitted.

The control section 10 of the ECU 1 c controls the operations of thevarious components by virtue of the supply of power received from apower supply apparatus, such as a battery or an alternator of a vehicle,not shown.

The storage section 11 uses a volatile memory, and the control section10 temporarily stores, in the storage section 11, various kinds ofinformation generated during processing, measurement values representedby signals input from a sensor as described later or data received fromthe relay apparatus 3 b.

The communication control section 12 has the function of a networkcontroller and achieves communication with the branch line 2 c. Thecontrol section 10 of the ECU 1 c transmits and receives data via thecommunication control section 12.

The ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1 d, 1 d,. . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . configured as described abovecan transmit data containing numerical information on various kinds ofphysical quantities, such as measurement values, calculation values andcontrol values, or can control the engine, brake, etc. usingmicrocomputers. For example, the ECU 1 c serves as an ABS (AntilockBrake System) and is connected to a sensor (not shown) for detecting therotation speed of a wheel (wheel speed). The ECU 1 c controls the brakeon the basis of the wheel speed detected via the sensor at the brakingof the vehicle and transmits the measurement value of the wheel speed asdata to the relay apparatus 3 b via the branch line 2 c.

Data transmitted from the ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c,1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . isformed of a pair of an attribute ID (identification data) foridentifying the attribute of data, such as wheel speed, temperature orangle, and specific numerical information (attribute value) of theattribute ID. For example, data representing a wheel speed consists of apair of an attribute ID “10” assigned to the wheel speed and anattribute value “3000 (rpm: revolutions per minute).” Furthermore, thenumerical information also includes control values, represented bynumerical information, for switching between on and off and among high,middle and low (on: 1, off: 0; high: 1, middle: 0, low: −1).

Moreover, data transmission and reception between the ECUs 1 a, 1 a, . .. , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . .. , 1 f, 1 f, . . . and the relay apparatuses 3 a, 3 b and 3 c arecarried out by transmitting and receiving a “message” consisting of aplurality of pieces of data. The ECUs 1 a, 1 b, 1 c, 1 d, 1 e, 1 ftransmit data groups obtained by their own operations as a messages whentransmitting data through the communication control section 12.

The communication lines (branch lines) 2 c and 2 d are communicationlines based on the CAN protocol, and the respective communicationcontrol sections 12 of the ECUs 1 c, 1 c, . . . and 1 d, 1 d, . . .transmit and receive messages on the basis of the CAN protocol via thebranch lines 2 c and 2 d, respectively. In the case of transmitting amessage on the basis of the CAN protocol, the ECUs 1 c, 1 c, . . . , 1d, 1 d, . . . transmit the message containing a message ID, i.e., “CANID”, specified for each combination of a plurality of pieces of datatogether with a group of attribute values corresponding to thecombination.

Without being limited to this, the branch lines 2 c and 2 d may becapable of transmitting and receiving messages on the basis of protocolssuch as LIN (Local Interconnect Network), FlexRay (registeredtrademark), etc. The other branch lines 2 a, 2 b, 2 e and 2 f aresimilar to the branch lines 2 c and 2 d. The branch lines 2 a, 2 b, 2 c,2 d, 2 e and 2 f may be formed of communication lines based on protocolsdifferent from each other depending on the type of data transmitted toand received from the ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c,. . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . .

The relay apparatus 3 b is equipped with a control section 30 b forcontrolling the operations of the respective components; a branchcommunication section 32 b connected to the branch lines 2 c and 2 d; afirst trunk communication section 33 b and a second trunk communicationsection 34 b connected to the trunk lines 4; a temporary storage area 35b formed of a volatile memory, such as a DRAM (Dynamic Random AccessMemory) or an SRAM (Static Random Access Memory); and a storage section36 b formed of a nonvolatile memory, such as an EPROM (ErasableProgrammable Read-Only Memory), an EEPROM (Electrically EPROM) or aflash memory. Since internal configurations of the relay apparatuses 3 aand 3 c are similar to that of the relay apparatus 3 b, the detaileddescriptions thereof are omitted.

The control section 30 b uses an MPU (Micro Processing Unit) and isconfigured so as to control the operations of the respective componentsby virtue of the supply of power received from a power supply apparatus,such as the alternator or the battery of the vehicle, not shown.

The branch communication section 32 b achieves data transmission to andreception from the ECUs 1 c, 1 c, . . . , 1 d, 1 d, . . . connectedthereto via the branch lines 2 c and 2 d. As described above, the datatransmission and reception between the ECUs 1 c, 1 c, . . . , 1 d, 1 d,. . . and the relay apparatus 3 b are carried out by the transmissionand reception of messages. Furthermore, the branch communication section32 b has a plurality of ports and is configured so as to be capable oftransmitting and receiving messages simultaneously via the respectiveports. The branch communication section 32 b provided for the relayapparatus 3 b according to the present embodiment has eight ports andcan transmit and receive messages simultaneously via the eight ports.

The first trunk communication section 33 b and the second trunkcommunication section 34 b achieve communication with the other relayapparatus 3 a and 3 c connected thereto via the trunk lines 4. The relayapparatus 3 b can communicate with the relay apparatus 3 a through thefirst trunk communication section 33 b and can also communicate with therelay apparatus 3 c through the second trunk communication section 34 b.The control section 30 b can simultaneously carry out communication withthe relay apparatus 3 a through the first trunk communication section 33b and communication with the relay apparatus 3 c through the secondtrunk communication section 34 b.

The control section 30 b communicates with the other relay apparatuses 3a and 3 c through the first trunk communication section 33 b and thesecond trunk communication section 34 b periodically at a regular periodof 1 ms for example.

The relay apparatus 3 a is also equipped with a first trunkcommunication section 33 a and a second trunk communication section 34a, and the communication sections can carry out communicationsimultaneously. In the present embodiment, the relay apparatus 3 a isconnected to the relay apparatus 3 b via the trunk line 4 through thesecond trunk communication section 34 a. Since the relay apparatus 3 ais not connected to a relay apparatus other than the relay apparatus 3b, the first trunk communication section 33 a is not used. Furthermore,the relay apparatus 3 c is also equipped with a first trunkcommunication section 33 c and a second trunk communication section 34c. However, in the present embodiment, the relay apparatus 3 c isconnected to the relay apparatus 3 b via the trunk line 4 through thefirst trunk communication section 33 c, and the second trunkcommunication section 34 c is not used. In the case that another relayapparatus is further connected to the relay apparatus 3 c, aconfiguration may be formed in which said another relay apparatus isconnected in a daisy-chain manner using the second trunk communicationsection 34 c so that the relay apparatus 3 c achieves communication withthe relay apparatus 3 b through the first trunk communication section 33c and communication with said another relay apparatus through the secondtrunk communication section 34 c.

The temporary storage area 35 b is provided with a storage area for thedatabase 31 b in which data is stored by the control section 30 b. Thedatabase 31 b may be provided in an area inside a storage unit locatedoutside of the relay apparatus 3 b and connected to the relay apparatus3 b so that data can be read and written. The temporary storage area 35b is provided with not only the database 31 b but also a storage areafor a receive buffer 37 b for temporarily storing received data(messages).

A correspondence table 38 b that is referred to when the control section30 b communicates with the other relay apparatuses 3 a and 3 c throughthe first trunk communication section 33 b and the second trunkcommunication section 34 b is stored beforehand in the storage section36 b. The details of the correspondence table 38 b will be describedlater.

Communication processing between the ECUs 1 a, 1 a, . . . , 1 b, 1 b, .. . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, .. . and the relay apparatuses 3 a, 3 b and 3 c in the vehicle-mountedcommunication system configured as described above will be describedbelow.

FIG. 3 is a flowchart showing an example of a procedure to be done inthe case that the control section 30 b of the relay apparatus 3 bconstituting the vehicle-mounted communication system according to thepresent embodiment receives a message. Since procedures to be done bythe other control sections 30 a and 30 c of the relay apparatuses 3 aand 3 c are similar to that to be done by the control section 30 b ofthe relay apparatus 3 b, the detailed descriptions thereof are omitted.

The control section 30 b judges whether a message transmitted from anyof the ECUs 1 c, 1 c, . . . , 1 d, 1 d, . . . connected thereto via thebranch lines 2 c and 2 d has been received through the branchcommunication section 32 b (at step S11). In the case that the controlsection 30 b judges that no message has been received (NO at step S11),the control section 30 b returns the procedure to step S11.

In the case that the control section 30 b judges that a message has beenreceived (YES at step S11), the control section 30 b stores the receivedmessage once in the receive buffer 37 b (at step S12), therebycompleting the procedure to be done in the case that the message hasbeen received.

An attribute value group contained in the message stored in the receivebuffer 37 b is stored for each attribute value ID at a timing describedlater. In other words, data consisting of a pair of an attribute valueID and an attribute value is stored in the database 31 b. The controlsection 30 b creates a message from the attribute value group of thedata stored in the database 31 b and transmits the message as necessaryto the ECUs 1 c, 1 c, . . . , 1 d, 1 d, . . . requiring the messagethrough the branch communication section 32 b. The timing of thetransmission is scheduled for each of the destination ECUs 1 c, 1 c, . .. , 1 d, 1 d, . . . , for example. The control section 30 b may create amessage by referring to the schedule stored in the storage section 36 band may transmit the message. Alternatively, the control section 30 bmay monitor the attribute value stored in the database 31 b and maytransmit the message containing the attribute value to the ECUs 1 c, 1c, . . . , 1 d, 1 d, . . . requiring the message in the case that theattribute value is changed by the renewal of the database 31 b.

Next, processing to be carried out when the control section 30 b of therelay apparatus 3 b communicates with the other relay apparatuses 3 aand 3 c through the first trunk communication section 33 b and thesecond trunk communication section 34 b will be described below.

When exchanging data stored in the database 31 b with data stored in theother relay apparatuses 3 a and 3 c, the control section 30 b does notread data consisting of a pair of an attribute value ID and an attributevalue from the database 31 b to transmit the data, but carries outtransmission and reception using the message stored once in the receivebuffer 37 b. More specifically, data is transmitted using a framecontaining gathered messages. The frame that is used at this time ishereafter referring to as a trunk frame.

A trunk frame using messages is transmitted for the following reason:since a message to be transmitted and received according to CAN isformed of one or a plurality of combinations of attribute values and aCAN ID is specified for each combination, the transmission of theattribute value ID for each attribute value can be omitted. It may bepossible that a data frame in which attribute value groups are gatheredmore efficiently than the messages transmitted from the ECUs 1 c, 1 c, .. . , 1 d, 1 d, . . . is specified, and a data frame ID may be specifieddepending on the number of attribute values contained in the data frameand their attribute value IDs.

FIGS. 4A and 4B are explanatory views showing format examples of a trunkframe transmitted by the control sections 30 a, 30 b and 30 c of therelay apparatuses 3 a, 3 b and 3 c constituting the vehicle-mountedcommunication system according to the present embodiment. FIG. 4A showsa format example of a trunk frame transmitted by the control sections 30a, 30 b and 30 c of the relay apparatuses 3 a, 3 b and 3 c according tothe present embodiment. FIG. 4B shows for comparison a format example inthe case of the transmission of a plurality of data formed of anattribute value ID and an attribute value.

As shown in FIG. 4A, the format of the trunk frame is formed such that aheader is added to the head of the trunk frame and a trailer indicatingthe end of the trunk frame is added to the end thereof. Furthermore, mmessages received by the relay apparatus 3 a from the ECUs 1 a, 1 a, . .. , 1 b, 1 b, . . . and stored in the receive buffer 37 a of the relayapparatus 3 a are contained between the header and the trailer of thetrunk frame to be transmitted from the relay apparatus 3 a. Moreover,each message contains a message ID (CAN ID) predetermined depending onthe number of attribute value groups and the combination of attributevalue IDs and also contains the total size (information length) of theattribute value groups following immediately thereafter. In this case,the maximum total size of the attribute value groups contained in themessage is eight bytes. In addition, a field itself representing thesize (information length) of the field of the attribute value groups inbyte units consists of four bits because eight should only berepresented at the maximum. Since the CAN ID is represented by 11 bits,the size of one message is 10 bytes when rounded up to bytes.

FIG. 4B shows for comparison with FIG. 4A a format example in the caseof the transmission of a plurality of data formed of an attribute valueID and an attribute value. Also in this case, a header is added to thehead and a trailer indicating the end of the transmission is added tothe end. In the case that k attribute values are contained in a messagereceived from the ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . by the relayapparatus 3 a and stored in the receive buffer 37 a, k pairs of anattribute value ID and an attribute value are contained between theheader and the trailer. In this case, it is assumed that the attributevalue ID is represented by two bytes.

FIG. 5 is an explanatory view showing examples of contents of thecorrespondence table 38 b stored in the storage section 36 b of therelay apparatus 3 b constituting the vehicle-mounted communicationsystem according to the present embodiment. In FIG. 5, n is an arbitrarynatural number. As shown in the explanatory view of FIG. 5, the numberof attribute values contained in a message and an attribute value IDcontained in the message, the position (order) of the attribute value inthe message and the information length (bit units) of the attributevalue for each attribute value are stored in the table so as tocorrespond to a message ID. An example of a content in FIG. 5 indicatesthat “two” attribute values are contained in the message having amessage ID of “1”. With respect to the first attribute value containedin the message having a message ID of “1”, the attribute value IDthereof is “1” and the attribute value has an information length of “1”bit and is contained at the “first” position, and with respect to thesecond attribute value, the attribute value ID thereof is “2”, and theattribute value has an information length of “1” bit and is contained atthe “second” position.

Another example of a content in FIG. 5 indicates that “four” attributevalues are contained in the message having a message ID of “2”. Withrespect to the first attribute value contained in the message having amessage ID of “2”, the attribute value ID thereof is “20” and theattribute value has an information length of “1” bit and is contained atthe “second” position, and with respect to the second attribute value,the attribute value ID thereof is “50”, and the attribute value has aninformation length of “8” bits and is contained at the “fourth”position. A still another example indicates that “n” attribute valuesare contained in the message having a message ID of “3”. With respect tothe first attribute value contained in the message having a message IDof “3”, the attribute value ID thereof is “8” and the attribute valuehas an information length of “3” bit and is contained at the “fourth”position, and with respect to the second attribute value, the attributevalue ID thereof is “5”, and the attribute value has an informationlength of “4” bits and is contained at the “n-th” position. Furthermore,a yet another example indicates that “64” attribute values are containedin the message having a message ID of “4”. With respect to the firstattribute value contained in the message having a message ID of “4”, theattribute value ID thereof is “1” and the attribute value has aninformation length of “1” bit and is contained at the “first” position,and with respect to the second attribute value, the attribute value IDthereof is “2”, and the attribute value has an information length of “1”bit and is contained at the “second” position.

Upon reception of a trunk frame having such a format as shown in FIG.4A, the control sections 30 a, 30 b and 30 c of the relay apparatuses 3a, 3 b and 3 c refer to the correspondence tables 38 a, 38 b and 38 c,respectively on the basis of the message IDs, and read attribute values.Hence, the relay apparatuses 3 a, 3 b and 3 c carry out transmission andreception using messages containing only attribute values withoutcontaining attribute value IDs. The control sections 30 a, 30 b and 30 cof the relay apparatuses 3 a, 3 b and 3 c can recognize attribute valuescontained in the messages and read the attribute values.

FIGS. 6 and 7 are flowcharts showing an example of a procedure in whichtrunk frames are transmitted and received among the relay apparatuses 3a, 3 b and 3 c constituting the vehicle-mounted communication systemaccording to the present embodiment. In the relay apparatuses 3 a, 3 band 3 c connected in a daisy-chain manner, the procedure described belowis repeated periodically, with the relay apparatus 3 a as a start point,at a regular period of 1 ms for example.

When the period is reached, the control section 30 a of the relayapparatus 3 a refers to the correspondence table 38 a of the storagesection 36 a and reads messages from the receive buffer 37 a in whichthe messages received from any of the ECUs 1 a, 1 a, . . . , 1 b, 1 b, .. . are temporarily stored (at step S201). The control section 30 a thencreates a trunk frame (at step S202) and transmits the created trunkframe to the relay apparatus 3 b through the second trunk communicationsection 34 b (at step S203).

The control section 30 b of the relay apparatus 3 b judges whether thetrunk frame has been received through the first trunk communicationsection 33 b (at step S204). In the case that the control section 30 bjudges that the trunk frame has not been received (NO at step S204), thecontrol section 30 b returns the procedure to step S204. In the casethat the control section 30 b judges that the trunk frame has beenreceived (YES at step S204), the control section 30 b reads messagesfrom the receive buffer 37 b in which the messages received from any ofECUs 1 c, 1 c, . . . , 1 d, 1 d, . . . are temporarily stored (at stepS205), and then creates a trunk frame to which the read messages areadded (at step S206). The control section 30 b of the relay apparatus 3b transmits the created trunk frame to the relay apparatus 3 c throughthe second trunk communication section 34 b (at step S207).

The control section 30 c of the relay apparatus 3 c judges whether thetrunk frame has been received through the first trunk communicationsection 33 c (at step S208). In the case that the control section 30 cjudges that the trunk frame has not been received (NO at step S208), thecontrol section 30 c returns the procedure to step S208. In the casethat the control section 30 c judges that the trunk frame has beenreceived (YES at step S208), the control section 30 c reads messagesfrom the receive buffer 37 c in which the messages received from any ofECUs 1 e, 1 e, . . . , 1 f, 1 f, . . . are temporarily stored (at stepS209), and then creates a trunk frame to which the read message is added(at step S210).

Since the relay apparatus 3 c is located at the end point of thedaisy-chain connection of the relay apparatuses 3 a, 3 b and 3 c, in thecase that the control section 30 c of the relay apparatus 3 c hasreceived the trunk frame from the relay apparatus 3 b, it is assumedthat the relay apparatus 3 c has obtained the messages stored in thereceive buffers 37 a, 37 b and 37 c of all the relay apparatuses 3 a, 3b and 3 c. Hence, the control section 30 c of the relay apparatus 3 cadds its own message to the received trunk frame and reads the attributevalues from the message group of the trunk frame to which the message isadded by referring to the correspondence table 38 c (at step S211) andrenews the database 31 c of the relay apparatus 3 c using the readattribute values (at step S212). Furthermore, the control section 30 cof the relay apparatus 3 c transmits the created trunk frame to therelay apparatus 3 b through the first trunk communication section 33 c(at step S213).

After transmitting the trunk frame created by the control section 30 b(at step S207), the control section 30 b of the relay apparatus 3 bjudges whether the trunk frame has been received from the relayapparatus 3 c through the second trunk communication section 34 b (atstep S214).

Since the relay apparatuses 3 a, 3 b and 3 c are connected indaisy-chain manner, the trunk frame transmitted from the relay apparatus3 c located at the end point of the connection has a meaning ofacknowledgement indicating that the trunk frames transmitted by therelay apparatuses 3 a and 3 b themselves have reached the relayapparatus 3 c located at the end point.

In the case that the control section 30 b of the relay apparatus 3 bjudges that the trunk frame has not been received from the relayapparatus 3 c through the second trunk communication section 34 b (NO atstep S214), the control section 30 b returns the procedure to step S214and waits. In the case that the control section 30 b judges that thetrunk frame has been received from the relay apparatus 3 c through thesecond trunk communication section 34 b (YES at step S214), since thereceived trunk frame contains the messages stored in the receive buffers37 a, 37 b and 37 c of all the relay apparatuses, i.e., the relayapparatus 3 a, the relay apparatus 3 b itself and the relay apparatus 3c, the control section 30 b reads attribute values from the messagegroup of the trunk frame by referring to the correspondence table 38 b(at step S215). Furthermore, the control section 30 b of the relayapparatus 3 b renews the database 31 b of the relay apparatus 3 b usingthe read attribute values (at step S216). Moreover, the control section30 b of the relay apparatus 3 b transmits the trunk frame received fromthe relay apparatus 3 c to the relay apparatus 3 a through the firsttrunk communication section 33 b (at step S217).

After transmitting the trunk frame created by the control section 30 a(at step S203), the control section 30 a of the relay apparatus 3 ajudges whether the trunk frame has been received from the relayapparatus 3 b through the second trunk communication section 34 a (atstep S218). The trunk frame transmitted from the relay apparatus 3 b hasa meaning of acknowledgement indicating that the trunk frame transmittedby the relay apparatus 3 a itself has reached the relay apparatus 3 clocated at the end point.

In the case that the control section 30 a of the relay apparatus 3 ajudges that the trunk frame has not been received from the relayapparatus 3 b through the second trunk communication section 34 a (NO atstep S218), the control section 30 a returns the procedure to step S218and waits. In the case that the control section 30 a judges that thetrunk frame has been received from the relay apparatus 3 b through thesecond trunk communication section 34 a (YES at step S218), since thereceived trunk frame contains the messages stored in the receive buffers37 a, 37 b and 37 c of all the relay apparatuses, i.e., the relayapparatus 3 a itself, the relay apparatus 3 b and the relay apparatus 3c, the control section 30 a reads attribute values from the messagegroup of the trunk frame by referring to the correspondence table 38 a(at step S219), and renews the database 31 a of the relay apparatus 3 ausing the read attribute values (at step S220), thereby completing theprocedure.

Next, the procedure shown in the flowcharts of FIGS. 6 and 7 will bedescribed below using a specific example. FIG. 8 is an explanatory viewschematically showing a process in which the databases 31 a, 31 b and 31c of the relay apparatuses 3 a, 3 b and 3 c according to the presentembodiment are renewed by the transmission and reception of trunkframes.

The explanatory view of FIG. 8 is a block diagram showing thedaisy-chain connection of the relay apparatuses 3 a, 3 b and 3 c and theconfigurations of the databases 31 a, 31 b and 31 c and the receivebuffers 37 a, 37 b and 37 c of the respective relay apparatuses 3 a, 3 band 3 c. As described above, the relay apparatus 3 a is used as thestart point and the relay apparatus 3 c is used as the end point.Furthermore, the explanatory view of FIG. 8 chronologically shows howthe trunk frames are transmitted and received by carrying out theprocedure shown in the flowcharts of FIGS. 6 and 7 using the controlsections 30 a, 30 b and 30 c of the relay apparatuses 3 a, 3 b and 3 c.

As shown in the flowcharts of FIGS. 6 and 7, a trunk frame, whichcontains an attribute value group A since a plurality of messages arecontained in the trunk frame, is transmitted from the relay apparatus 3a used as the start point to the relay apparatus 3 b via the trunk line4. In the case that the trunk frame transmitted from the relay apparatus3 a is received by the relay apparatus 3 b, the trunk frame to which anattribute value group B is added and which contains the attribute valuegroup A is transmitted from the relay apparatus 3 b to the relayapparatus 3 c via the trunk line 4. In the case that the trunk frametransmitted from the relay apparatus 3 b and containing the attributevalue groups A and B is received by the relay apparatus 3 c, theattribute value groups A and B are added to the trunk frame containingattribute value group C. This creates a trunk frame containing theattribute value groups A, B and C of the data received from the ECUs 1a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1e, 1 e, . . . , 1 f, 1 f, . . . and stored in the receive buffers 37 a,37 b and 37 c of all the relay apparatuses, i.e., the relay apparatuses3 a, 3 b and 3 c.

In the relay apparatus 3 c located at the end point, the database 31 cis renewed using the attribute values read from the trunk framecontaining the attribute value groups A, B and C. The trunk framecontaining the attribute value groups A, B and C is transmitted from therelay apparatus 3 c to the relay apparatus 3 b and from relay apparatus3 b to the relay apparatus 3 a. Also in the relay apparatus 3 b and therelay apparatus 3 a, the databases 31 b and 31 a are renewed in thisorder using the attribute values read from the trunk frame containingthe attribute value groups A, B and C.

Since the databases 31 a, 31 b and 31 c are renewed using the attributevalues read from trunk frames containing the attribute value groups A, Band C and having the same contents, the contents of the databases 31 a,31 b and 31 c are synchronized to the same contents. When transmittingdata to the ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, . . . , the relayapparatuses 3 a, 3 b and 3 c transmit data formed of the attributevalues read from the databases 31 a, 31 b and 31 c in the form of beingcontained in messages. As a result, even the ECUs 1 a, 1 a, . . . , 1 b,1 b, . . . , 1 c, 1 c, . . . , 1 d, 1 d, . . . , 1 e, 1 e, . . . , 1 f,1 f, . . . connected to the different branch lines 2 a, 2 b, 2 c, 2 d, 2e and 2 f receive the same attribute values. In other words, it ispossible to avoid a situation in which the specific values of the wheelspeeds received by the ECUs 1 b and 1 c respectively connected to thedifferent branch lines 2 b and 2 c are respectively 3000 (rpm) and 2500(rpm), for example, thus different from each other.

Furthermore, since the present embodiment is configured so that thecommunication among the relay apparatuses 3 a, 3 b and 3 c via the trunklines 4 is carried out according to the format of the trunk frame inwhich a plurality of messages containing a plurality of attribute valuegroups are further contained, the transmission and reception of anattribute value ID for each attribute value is omitted, whereby theamount of communication is reduced. The effect of the reduction in theamount of communication will be described below by giving specificvalues.

The relay apparatuses 3 a, 3 b and 3 c repeat the procedure shown in theflowcharts of FIGS. 6 and 7 every 1 ins and transmit and receive thetrunk frames as shown in the explanatory view of FIG. 8. A case in whicha message containing 64 one-bit attribute values is received four timesat the eight ports of the respective branch communication sections 32 a,32 b and 32 c of the relay apparatuses 3 a, 3 b and 3 c until the periodof 1 ms is reached is taken as an example and described below.

When the relay apparatus 3 a used as the start point creates a trunkframe, 2048 (=8 ports×4 messages (the number of messages per port)×64(the number of attribute values contained in one message)) one-bitattribute values are stored in each of the receive buffers 37 a, 37 band 37 c.

The amount of communication required when the relay apparatus 3 atransmits attribute values to the relay apparatus 3 b using the trunkframe shown in FIG. 4A is calculated using the following expression 1.In this case, it is assumed that 64 one-bit attribute values (eightbytes) are contained in one message. Hence, one trunk frame containing32 messages is transmitted.

$\begin{matrix}{{\{ {( {{ID\_ L} + {DLC\_ L} + {D\_ L}} ) \times m} \} + {H\_ L} + {T\_ L}} = {{\{ {( {{11\mspace{11mu}({bits})} + {4\mspace{11mu}({bits})} + {8\mspace{11mu}({bytes})}} ) \times 32} \} + {H\_ L} + {T\_ L}} = \{ {{( {10\mspace{11mu}({bytes}) \times 32} \} + {H\_ L} + {T\_ L}} = {{320\mspace{11mu}({bytes})} + {H\_ L} + {T\_ L}}} }} & (1)\end{matrix}$wherein

ID_L: the information length of a message ID

DLC_L: the information length of a field representing the informationlength of an attribute value group

D_L: the information length of an attribute value group

m: the number of messages

H_L: the information length of a header

T_L: the information length of a trailer

Hence, as shown in the explanatory view of FIG. 8, the amount ofcommunication from the relay apparatus 3 a to the relay apparatus 3 b,from the relay apparatus 3 b to the relay apparatus 3 c, from the relayapparatus 3 c to the relay apparatus 3 b and from the relay apparatus 3b to the relay apparatus 3 a by the time when the databases 31 a, 31 band 31 c are synchronized is calculated using the following expression2.

$\begin{matrix}{{\{ {{1 \times 320\mspace{11mu}({bytes})} + {H\_ L} + {T\_ L}} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}{\mspace{11mu}\;}3a\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b} )} + {\{ {2 \times 320\mspace{11mu}({bytes})} \}\mspace{11mu}{\quad\;{( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b{\mspace{11mu}\;}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}{\mspace{11mu}\;}3c} ) + {\{ {3 \times 320\mspace{11mu}({bytes})} \}\;{\quad\;{\quad{\quad{( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3c\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\; 3b} ) + {\quad{{\quad\{ {3 \times 320\mspace{11mu}({bytes})} \}\quad}{\quad\;{\quad{( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3 b\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3a} ) = {{2880\mspace{11mu}({bytes})} + ( {{H\_ L} + {T\_ L}} )}}}}}}}}}}}}}}} & (2)\end{matrix}$

According to the expression 2, 2880 bytes of information is required tobe transmitted and received via the trunk lines 4 within the period ofevery 1 ins. In the case that the communication speed of the trunk line4 is 100 Mbps, the time required for the transmission and reception of2880 bytes of information is approximately 230 μs. The transmission andreception of 2880 bytes of information can be carried out sufficientlywithin the period of every 1 ms.

For comparison, as shown in FIG. 4B, in the case of a configuration inwhich the relay apparatus 3 a transmits attribute values to the relayapparatus 3 b using a format containing pairs of an attribute value IDand an attribute value, the number of the pairs being equal to thenumber of the attribute values, the amount of communication required fortransmission from the relay apparatus 3 a used as the start point to therelay apparatus 3 b is calculated according to the following expression3.

$\begin{matrix}{{\{ {( {{{Information}\mspace{14mu}{length}\mspace{14mu}{of}\mspace{14mu}{attribute}\mspace{14mu}{value}\mspace{14mu}{ID}} + {{information}\mspace{14mu}{length}\mspace{14mu}{of}\mspace{14mu}{attribute}\mspace{14mu}{value}}} ) \times {number}\mspace{14mu}{of}\mspace{14mu}{attribute}\mspace{14mu}{values}} \} + {{information}\mspace{14mu}{length}\mspace{14mu}{of}\mspace{14mu}{header}} + {{information}\mspace{14mu}{length}\mspace{14mu}{of}\mspace{14mu}{trailer}}} = {{\{ {( {{2\mspace{11mu}({bytes})} + {1\mspace{11mu}({bit})}} ) \times 2048} \} + {h\_ L} + {t\_ L}} = {{4352\mspace{11mu}({bytes})} + {h\_ L} + {t\_ L}}}} & (3)\end{matrix}$wherein

h_L: the information length of the header

t_L: the information length of the trailer

Hence, the amount of communication from the relay apparatus 3 a to therelay apparatus 3 b, from the relay apparatus 3 b to the relay apparatus3 c, from the relay apparatus 3 c to the relay apparatus 3 b and fromthe relay apparatus 3 b to the relay apparatus 3 a is calculated usingthe following expression 4.

$\begin{matrix}{{{\{ {{1 \times 4352\mspace{11mu}({bytes})} + {h\_ L} + {t\_ L}} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3a\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b} )} + {\{ {2 \times 4352\mspace{11mu}({bytes})} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}{\mspace{11mu}\;}3c} )} + {\{ {3 \times 4352\mspace{11mu}({bytes})} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3c\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b} )} + {\{ {3 \times 4352\mspace{11mu}({bytes})} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3a} )}} = {{39168\mspace{11mu}({bytes})} + ( {{h\_ L} + {t\_ L}} )}} & (4)\end{matrix}$

According to the expression 4, 39168 bytes of information is required tobe transmitted and received via the trunk lines 4 within the period ofevery 1 ms. In the case that the communication speed of the trunk line 4is 100 Mbps, the time required for the transmission and reception of39168 bytes of information is 3 ms. Hence, the transmission andreception of the information cannot be carried out within the period ofevery 1 ms.

In the case that data is transmitted and received so that the contentsof the databases 31 a, 31 b and 31 c are synchronized among the relayapparatuses 3 a, 3 b and 3 c, a trunk frame having such a format asshown in FIG. 4A is created and then transmitted and received, wherebythe amount of communication among the relay apparatuses 3 a, 3 b and 3 ccan be reduced up to approximately 1/10. As a result, the time requiredfor the synchronization of the databases 31 a, 31 b and 31 c among therelay apparatuses 3 a, 3 b and 3 c can be reduced, and thesynchronization can be completed at high speed. Furthermore, it ispossible to ensure the uniformity of data and the immediacy of relayamong the ECUs 1 a, 1 a, . . . , 1 b, 1 b, . . . , 1 c, 1 c, . . . , 1d, 1 d, . . . , 1 e, 1 e, . . . , 1 f, 1 f, connected to the differentbranch lines 2 a, 2 b, 2 c, 2 d, 2 e and 2 f.

In the configuration of the above-mentioned vehicle-mountedcommunication system, data is relayed via the three relay apparatuses 3a, 3 b and 3 c. However, even in the case of a configuration in which,for example, five relay apparatuses are connected in a daisy-chainmanner, the amount of communication required for the transmission andreception in the period of every 1 ms is 9600 bytes. When thecommunication speed of the trunk line is 100 Mbps, the time required forthe transmission and reception is approximately 770 μs, whereby thetransmission and reception can be carried out within the period.

In the above-mentioned descriptions, the three relay apparatuses 3 a, 3b and 3 c are configured so that the transmission and reception of trunkframes can be carried out cyclically from the relay apparatus 3 a to therelay apparatus 3 b, from the relay apparatus 3 b to the relay apparatus3 c, from the relay apparatus 3 c to the relay apparatus 3 b and therelay apparatus 3 b to the relay apparatus 3 a. However, the relayapparatus 3 b can carry out transmission and reception simultaneouslythrough the first trunk communication section 33 b and the second trunkcommunication section 34 b. Hence, the relay apparatus 3 b may carry outthe transmission of trunk frames without waiting for the reception oftrunk frames from the other relay apparatuses 3 a and 3 c.

FIG. 9 is a flowchart showing another example of the procedure in whichtrunk frames are transmitted and received among the relay apparatuses 3a, 3 b and 3 c constituting the vehicle-mounted communication systemaccording to the present embodiment. The flowchart of FIG. 9 shows aprocedure to be done by the control section 30 b of the relay apparatus3 b. Since the procedures to be done by the control sections 30 a and 30c of the other relay apparatuses 3 a and 3 c are similar to that to bedone by the control section 30 b, the detailed descriptions thereof areomitted.

The relay apparatus 3 b repeats the procedure described belowperiodically at a regular period of 1 ms.

When the period is reached, the control section 30 b refers to thecorrespondence table 38 b of the storage section 36 b and reads messagesfrom the receive buffer 37 b in which the messages received from theECUs 1 c, 1 c, . . . , 1 d, 1 d, . . . are temporarily stored (at stepS301), and the control section 30 b creates a trunk frame containing themessages received from the ECUs 1 c, 1 c, . . . , 1 d, 1 d, . . . (atstep S302).

The control section 30 b judges whether the reception of a trunk framefrom either of the other relay apparatuses 3 a and 3 c has been startedthrough the first trunk communication section 33 b or the second trunkcommunication section 34 b or whether the relay apparatus 3 b has atrunk frame to be transmitted and the trunk frame can be transmittedthrough the first trunk communication section 33 b or the second trunkcommunication section 34 b (at step S303). The control section 30 b cansimultaneously carry out transmission or reception through the firsttrunk communication section 33 b and transmission or reception throughthe second trunk communication section 34 b.

In the case that the reception of a trunk frame has not been startedfrom the first trunk communication section 33 b or the second trunkcommunication section 34 b and that the relay apparatus 3 b has no trunkframe to be transmitted (NO at step S303), the control section 30 breturns the procedure to step S303.

In the case that the control section 30 b judges that the reception of atrunk frame has started from either of the other relay apparatuses 3 aand 3 c through the first trunk communication section 33 b or the secondtrunk communication section 34 b or whether the relay apparatus 3 b hasa trunk frame to be transmitted and the trunk frame can be transmittedthrough the first trunk communication section 33 b or the second trunkcommunication section 34 b (YES at step S303), the control section 30 bjudges whether the trunk frame has been received (at step S304). In thecase that the control section 30 b judges that the trunk frame has beenreceived (YES at step S304), the control section 30 b temporarily storesthe received trunk frame in the temporary storage area 35 b (at stepS305).

In the case that the control section 30 b judges that no trunk frame hasbeen received at step S304 (NO at step S304), the control section 30 bjudges whether the trunk frame can be transmitted through the firsttrunk communication section 33 b or the second trunk communicationsection 34 b (at step S306). In the case that the control section 30 bjudges that the trunk frame cannot be transmitted (NO at step S306), thecontrol section 30 b returns the procedure to step S303. In the casethat the control section 30 b judges that the trunk frame can betransmitted (YES at step S306), the control section 30 b transmits thetrunk frame created by itself or the trunk frame received from any ofthe other relay apparatuses 3 a and 3 c and temporarily stored so as tobe transmitted to the others (at step S307).

In the case that the control section 30 b judges that no trunk frame hasbeen received at step S304, the procedure is advanced to step S306.However, the control section 30 b can simultaneously carry outtransmission or reception through the first trunk communication section33 b and transmission or reception through the second trunkcommunication section 34 b. Hence, while receiving the trunk framethrough the first trunk communication section 33 b, the control section30 b can transmit the trunk frame through the second trunk communicationsection 34 b. For this reason, even in the case that the control section30 b judges that a trunk frame has been received through the first trunkcommunication section 33 b or the second trunk communication section 34b (YES at step S304), the control section 30 b advances the procedure tostep S306 while the control section 30 b receives and temporarily storesthe trunk frame (at step S305). In the case that the first trunkcommunication section 33 b or the second trunk communication section 34b is not used and a trunk frame to be transmitted is present, thecontrol section 30 b transmits the trunk frame (at step S307).

Next, the control section 30 b judges whether all the trunk framestransmitted from the other relay apparatuses 3 a and 3 c and the trunkframe created by itself has been transmitted and received (at stepS308). In the case that the control section 30 b judges that all thetrunk frames have not been transmitted and received (NO at step S308),the control section 30 b returns the procedure to step S303.

In the case that the control section 30 b judges that all the trunkframes have been transmitted and received (YES at step S308), thecontrol section 30 b reads the attribute values from the message groupscontained in the trunk frames received and temporarily stored and thetrunk frame created by itself by referring to the correspondence table38 b (at step S309). The control section 30 b then renews the database31 b of the relay apparatus 3 b using the read attribute values (at stepS310) and completes the procedure.

FIG. 10 is an explanatory view schematically showing another example ofthe process in which the databases 31 a, 31 b and 31 c of the relayapparatuses 3 a, 3 b and 3 c according to the present embodiment arerenewed by the transmission and reception of trunk frames.

The explanatory view of FIG. 10 is a block diagram showing thedaisy-chain connection of the relay apparatuses 3 a, 3 b and 3 c and theconfigurations of the databases 31 a, 31 b and 31 c and the receivebuffers 37 a, 37 b and 37 c of the relay apparatuses 3 a, 3 b and 3 c.Furthermore, the explanatory view of FIG. 10 chronologically shows howthe trunk frames are transmitted and received by the control section 30a, 30 b and 30 c of the relay apparatuses 3 a, 3 b and 3 c carrying outthe procedure shown in the flowcharts of FIG. 9.

As shown in the flowchart of FIG. 9, the relay apparatus 3 b can carryout transmission and reception simultaneously through either the firsttrunk communication section 33 b or the second trunk communicationsection 34 b. Hence, since the second trunk communication section 34 aof the relay apparatus 3 a is not used, during a period in which a trunkframe containing the attribute value group A read from the receivebuffer 37 a of the relay apparatus 3 a is transmitted to the relayapparatus 3 b via the trunk line 4, the relay apparatus 3 b transmitsthe trunk frame containing the attribute value group B to the relayapparatus 3 c while receiving the trunk frame containing the attributevalue group A.

Then, in the relay apparatus 3 b, while the trunk frame containing theattribute value group A received from the relay apparatus 3 a istransmitted from the relay apparatus 3 b to the relay apparatus 3 cthrough the second trunk communication section 34 b, the trunk framecontaining the attribute value group B is transmitted to the relayapparatus 3 a through the first trunk communication section 33 b.Furthermore, since the first trunk communication section 33 c of therelay apparatus 3 c is not used, the trunk frame containing theattribute value group C is transmitted from the relay apparatus 3 c tothe relay apparatus 3 b. At this time, since the control section 30 c ofthe relay apparatus 3 c receives the trunk frames from the other relayapparatuses 3 a and 3 b and transmits the trunk frame created by itself,the control section 30 c reads attribute values from the message groupsof all the trunk frames and renews the database 31 c.

At the next timing, the relay apparatus 3 b transmits the trunk framecontaining the attribute value group C received from another relayapparatus 3 c to the relay apparatus 3 a. Then, since the controlsection 30 b of the relay apparatus 3 b has received the trunk framesfrom the other relay apparatuses 3 a and 3 c and has transmitted thetrunk frame created by itself, the control section 30 b reads attributevalues from the message groups of all the trunk frames and renews thedatabase 31 b.

Moreover, when the control section 30 a of the relay apparatus 3 a hasreceived the trunk frame containing the attribute value group C from therelay apparatus 3 b, since the control section 30 a has received thetrunk frames from the other relay apparatuses 3 b and 3 c and hastransmitted the trunk frame created by itself, the control section 30 areads attribute values from the message groups of all the trunk framesand renews the database 31 a.

As a result, the contents of the databases 31 a, 31 b and 31 c aresynchronized so as to have the same contents. As shown in theexplanatory view of FIG. 10, the amount of communication in the casethat the trunk frames are transmitted and received among the relayapparatuses 3 a, 3 b and 3 c by the time when the databases 31 a, 31 band 31 c are synchronized is calculated using the following expression5.

$\begin{matrix}{{{\{ {{1 \times 320\mspace{11mu}({bytes})} + {H\_ L} + {T\_ L}} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3a\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b} )} + {\{ {{1 \times 320\mspace{11mu}({bytes})} + {H\_ L} + {T\_ L}} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b{\mspace{11mu}\;}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3c} )} + {\{ {{1 \times 320\mspace{11mu}({bytes})} + {H\_ L} + {T\_ L}} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3c\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}{\mspace{11mu}\;}3b} )} + {\{ {{1 \times 320\mspace{11mu}({bytes})} + {H\_ L} + {T\_ L}} \}\mspace{11mu}( {{from}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3b\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{relay}\mspace{14mu}{apparatus}\mspace{14mu} 3a} )}} = {{1280\mspace{11mu}({bytes})} + {4 \times ( {{H\_ L} + {T\_ L}} )}}} & (5)\end{matrix}$

In the explanatory view of FIG. 10, the transmission and reception oftrunk frames are carried out six times among the relay apparatuses 3 a,3 b and 3 c. However, each trunk frame is transmitted and received foreach of the attribute value groups A, B and C. Furthermore, thetransmission of the trunk frame containing the attribute value group Afrom the relay apparatus 3 a to the relay apparatus 3 b and thetransmission of the trunk frame containing the attribute value group Bfrom the relay apparatus 3 b to the relay apparatus 3 c are carried outsimultaneously. Moreover, the transmission of the trunk frame containingthe attribute value group A from the relay apparatus 3 b to the relayapparatus 3 c and the transmission of the trunk frame containing theattribute value group B from the relay apparatus 3 b to the relayapparatus 3 a are carried out simultaneously. Hence, the time requiredfor the synchronization of the databases 31 a, 31 b and 31 c during theperiod of every 1 ms is the time required for the transmission andreception of 1280 bytes of information via the trunk lines 4. Hence, thetime required for the synchronization is 102 μs. As a result, the timerequired for the synchronization of the databases 31 a, 31 b and 31 c isfurther reduced.

Although the vehicle-mounted communication system according to thepresent embodiment is configured such that when the control sections 30a, 30 b and 30 c of the relay apparatuses 3 a, 3 b and 3 c receive thetrunk frames, the control sections 30 a, 30 b and 30 c store thecorrespondence tables 38 a, 38 b and 38 c and refer to them, theconfiguration of the system is not limited to this configuration. Forexample, it may be possible to have a configuration in which the numberand order of messages and the combination and order of attribute valuesinside the messages contained in a trunk frame transmitted and receivedamong the relay apparatuses are predetermined for each of the relayapparatuses, and a relay apparatus having received the trunk framespecifies the relay apparatus from which the trunk frame has beentransmitted and reads the attribute values accurately.

The disclosed embodiment should be construed as exemplary rather than aslimitative of the present invention in all respects. The scope of thepresent invention is defined not by the above-mentioned descriptions butby the appended claims, and is intended to include all the modificationswithin the meaning and scope equivalent to the scope of the claims.

The invention claimed is:
 1. A relay apparatus connected to externalapparatuses for transmitting and receiving data containing numericalinformation and identification information of the numerical information,thereby relaying transmission and reception of data among externalapparatuses, comprising: a data receiving section that receives datafrom at least one of the external apparatuses; a data storing sectionthat stores data in a database; a data transmitting section thattransmits data read from the database to at least one of the externalapparatuses; a creating section that creates a data frame in which aplurality of pieces of numerical information on a plurality of pieces ofdata received from at least one of the external apparatuses arecontained and a plurality of pieces of identification informationcorresponding to each of the plurality of pieces of the numericalinformation are omitted; a data frame transmitting section thattransmits the data frame created by the creating section to anotherrelay apparatus; a data frame receiving section that receives a dataframe from another relay apparatus; a reading section that reads, in thecase that the data frame receiving section received a data frame, aplurality of pieces of numerical information contained in the receiveddata frame; and a renewing section that renews a plurality of pieces ofnumerical information on a plurality of pieces of data in the databaseaccording to the plurality of pieces of the numerical information readby the reading section.
 2. The relay apparatus according to claim 1,further comprising: an information prestoring section that prestorespositions and information lengths of the numerical information containedin a data frame for each number of pieces of numerical informationcontained in the data frame and each data type specified depending onidentification information corresponding to the numerical information,and identification information corresponding to the respective pieces ofthe numerical information; an information transmitting section thattransmits information on the type of data frame when the data frame istransmitted to another relay apparatus; and a specifying section thatspecifies, when data frame is received from another relay apparatus, thetype of the received data frame; wherein when a data frame is receivedfrom said another relay apparatus, a plurality of pieces of numericalinformation are derived from the data frame on the basis of the typespecified by the specifying section and the contents prestored in theinformation prestoring section.
 3. A communication system, comprising; aplurality of communication apparatus groups, each group being formed ofa plurality of communication apparatuses for transmitting and receivingdata containing numerical information and identification information ofthe numerical information; and a plurality of relay apparatuses to whichone or a plurality of communication apparatuses are connected in each ofthe plurality of communication apparatus groups, the plurality of relayapparatuses being connected mutually to relay transmission and receptionof data among the communication apparatuses; wherein each of the relayapparatuses includes: a data receiving section that receives data fromat least one of the communication apparatuses; a data storing sectionthat stores data in a database; a data transmitting section thattransmits data read from the database to at least one of thecommunication apparatuses; a creating section that creates a data framein which a plurality of pieces of numerical information on a pluralityof pieces of data received from at least one of the communicationapparatuses are contained and a plurality of pieces of identificationinformation corresponding to each of the plurality of pieces of thenumerical information is omitted; a data frame transmitting section thattransmits transmit the data frame created by the creating section toanother relay apparatus; a data frame receiving section that receives adata frame from another relay apparatus; a reading section that reads,in the case that the data frame receiving section received data frame, aplurality of pieces of numerical information contained in the receiveddata frame; and a renewing section that renews a plurality of pieces ofnumerical information on a plurality of pieces of data in the owndatabase of each relay apparatus using the plurality of pieces ofnumerical information read by the reading section.
 4. The communicationsystem according to claim 3 wherein connection topology among theplurality of relay apparatuses is daisy-chain topology.
 5. Thecommunication system according to claim 3, wherein each of the relayapparatuses further includes: an information prestoring section thatprestores positions and information lengths of the numerical informationcontained in a data frame for each number of pieces of numericalinformation contained in the data frame and each data type specifieddepending on identification information corresponding to the numericalinformation, and identification information corresponding to therespective pieces of the numerical information; an informationtransmitting section that transmits information on the type of dataframe when the data frame is transmitted to another relay apparatus; anda specifying section that specifies, when data frame is received fromanother relay apparatus, the type of the received data frame; whereinwhen a data frame is received from said another relay apparatus, aplurality of pieces of numerical information are derived from the dataframe on the basis of the type specified by the specifying section andthe contents prestored in the information prestoring section.
 6. Acommunication method using a plurality of relay apparatuses to which oneor a plurality of communication apparatuses are connected in each of aplurality of communication apparatus groups, each group being formed ofthe plurality of communication apparatuses for transmitting andreceiving data containing numerical information and identificationinformation of the numerical information and which are mutuallyconnected to relay transmission and reception of data amongcommunication apparatuses wherein each of the relay apparatusesperforms: receiving data from at least one of the communicationapparatuses of the group to which the relay apparatus is connected;storing data in a database; transmitting data read from the database toat least one of the communication apparatuses; creating a data frame inwhich a plurality of pieces of numerical information on a plurality ofpieces of data received from at least one of the communicationapparatuses are contained and a plurality of pieces of identificationinformation corresponding to each of the plurality of pieces of thenumerical information are omitted; transmits the created data frame toanother relay apparatus; reading, in the case that a data frame isreceived from another relay apparatus, a plurality of pieces ofnumerical information contained in the received data frame; renewing aplurality of pieces of numerical information on a plurality of pieces ofdata in the own database of each relay apparatus using the plurality ofpieces of the read numerical information; reading data from the reneweddatabase; and transmitting the read data to at least one of thecommunication apparatuses of the group to which the relay apparatus isconnected.
 7. The communication method according to claim 6, whereineach of the relay apparatuses further performs: prestoring positions andinformation lengths of the numerical information contained in a dataframe for each number of pieces of numerical information contained inthe data frame and each data type specified depending on identificationinformation corresponding to the numerical information, andidentification information corresponding to the respective pieces of thenumerical information; transmitting information on the type of dataframe when the data frame is transmitted to another relay apparatus;specifying, when data frame is received from another relay apparatus,the type of the received data frame; and deriving a plurality of piecesof numerical information from a data frame on the basis of the specifiedtype and the prestored contents, when the data frame is received fromsaid another relay apparatus.